This invention relates to a process for strengthening the lower shell of a sealed compressor housing.
Refrigerant compressors typically include a compressor pump driven by a motor within a sealed housing. In such compressors, the refrigerant is allowed to flow over the motor driving the compressor pump to cool the motor during operation. Therefore the sealed housing must provide a fluid tight seal. Most housings are constructed from upper and lower shells attached to corresponding ends of a center cylindrical shell. The motor and compressor are secured within the center shell.
One common type of compressor used for commercial and residential refrigeration applications is a scroll compressor. A scroll compressor operates by trapping refrigerant within compression chambers formed between interfitting scrolls. Each scroll has a generally spiral wrap extending from a base. Typically one of the scrolls is an orbiting scroll and the other is non-orbiting. The motor drives the orbiting scroll relative to the non-orbiting scroll to progressively reduce the volume of the compression chambers, thereby compressing the refrigerant.
In one recently developed lower shell, a guide portion engages an inner part of the center shell to align the two pieces. The guide portion has a u-shaped section formed in the lower shell. The guide portion of the lower section is typically formed from a cold forming process such as stamping. The stamping process introduces stresses into the lower shell that increases the brittleness of the material in sections having the most intricate shapes. The increase in brittleness corresponds to a reduction in material elongation properties caused by cold work hardening of the stamping process. Further, the center shell is attached to the lower shell by a welding process that creates heat-affected zones that further hardens the material.
Currently pending patent application Ser. No. 09/816,178 titled xe2x80x9cWeld Strengthening Component for Sealed Compressorsxe2x80x9d assigned to the applicant includes the addition of a strengthening member to the u-shaped section in order to increase the static pressure level that can be held by the sealed compressor. Such a method improves the static pressure capability of the sealed housing, however, it would be desirable to further increase this capability. Further, the addition of the strengthening member requires additional parts and manufacturing steps that may be undesirable in the cost conscious production environment.
Thus it would be desirable to strengthen the lower shell and particularly any region with dramatic and acute shapes such as the above-described u-shaped sections without additional parts.
A disclosed embodiment of this invention is a sealed compressor housing with a heat-treated lower shell that increases the capability of the sealed housing to withstand high static pressures.
The heat-treated lower shell is attached by a welding operation to a center shell. The lower shell of the subject compressor is heat treated to relieve stresses built up from previous processes. In the preferred embodiment the lower shell includes a u-shaped bend that is formed by a stamping process. The stamping process cold works the part and creates regions or zones of increased hardness. As the hardness of the material is increased the capability of the material to expand is decreased. This capability is related to elongation properties of the material.
The cold working process introduces high stress areas particularly in regions with the most dramatic changes in shape such as in the u-shaped guide section of the lower shell. Heat treatment of the lower shell relieves stress in the material and restores the materials elongation properties to a level substantially that of the original material. Heat-treating of the lower shell before the welding process restores the material to substantially the original elongation properties of the material such that stresses introduced by the welding process do not change the elongation properties of the material to the magnitude of the combined process without heat treat.
This invention provides a lower shell with improved material properties such that the static pressure capability of the sealed housing is significantly improved without additional parts or expensive additional manufacturing process.